Why would people want to wear misfitting clothing, why would people forgo cutting their hair, or choose to wear ridiculously heavy makeup, etc. It's an image, in this case an image of ~don give a fuck~ that she uses to appeal to the teenagers to whom she is marketed. You can see a logical strand between this, her manner of speaking, and her insistence that everything she does is somehow more 'real' than the things other actors/celebs do.